1. Field of the Invention
The present invention relates to a color thermal printer and color thermal printing method, and more particularly, relates to a color thermal printer and color thermal printing method for suppressing deviation of color registration.
2. Explanation of the Prior Art
One-pass type printing is used for a color thermal printer, in which full color image is recorded by executing thermal recording of yellow, magenta and cyan images in sequence when recording sheet passes a plurality of thermal heads. In one-pass type printing, full color image is printed on a plurality of recording areas which are serially provided in a feeding direction of recording sheet, and margins created between the recording areas are cut to produce a plurality of color prints.
In one-pass type color thermal printer, a plurality of thermal heads are serially pressed on recording sheet, so that tension imposed on recording sheet successively fluctuates. Accordingly, the transporting quantity and expansion and contraction quantities of recording sheet fluctuate, and inconsistency in density is likely to occur in printing by the thermal head disposed upstream. U.S. Pat. No. 6,474,886 discloses a color thermal printer of one-pass type, in which a couple of tension rollers are disposed close to each thermal head for imposing tension on recording sheet.
However, there occurs color registration deviation (hereinafter referred to as only a registration deviation) even for a color thermal printer, in which tensioning fluctuation of recording sheet during recording is suppressed by using such as the tension roller couple as described above. Particularly, the registration deviation occurs in continuous printing by such as a color thermal printer of one-pass type.